An active matrix liquid crystal display device includes a switching element for each pixel, and therefore can provide high-definition and high-quality display. As the switching element, a nonlinear element such as a thin film transistor (hereinafter, may be referred to as a “TFT”), a diode or the like is used. Among these elements, a TFT using amorphous silicon is widely used. In order to produce an active matrix liquid crystal display device at low cost, methods using a decreased number of photomasks (e.g., four-mask process) are now actively developed (e.g., Patent Document 1).
A production process of an active matrix liquid crystal display device usually includes many steps which are likely to cause electrostatic charges (e.g., rubbing step, etc.). However, a semiconductor device including a TFT is easily damaged by electrostatic charges. There is a problem that, for example, the electrostatic charges generated in a production process of a liquid crystal display device changes the TFT characteristic or causes electrostatic destruction, which reduces the yield.
In such a situation, active matrix substrates including various protection measures for preventing damage from being caused by electrostatic charges generated in a production process of a liquid crystal display device have been proposed or adopted (e.g., Patent Documents 2 through 4).